Keyboard having improved magnetic actuator

ABSTRACT

An improved key stem magnet for eliminating magnet migration in a key assembly employing a magnetic actuator. A magnet has a slotted portion extending longitudinally for providing a pair of abutment edges which engage opposing surfaces of a key stem. The abutment edges prevent axial migration of the magnet when mounted in an aperture in the key stem. A pair of parallel, axially extending magnet sidewalls located substantially opposite the slotted portion limit axial rotation of the magnet in the aperture.

United States atent 1 1 1 3,761,016 Peder-sen Sept. 25, 1973 [54] KEYBOARD HAVING IMPROVED 3,612,241 10/1971 Bemin 197/98 MAGNETIC ACTUATOR 3,698,531 10/1972 Bernin 197/98 Inventor: Egon A. lPedersen, Diablo, Calif.

The Singer Company, New York, NY.

Filed: Aug. 23, 11972 Appl. No.: 283,250

Assignee:

US. Cl

llnt. Cl. Field of Search 235/145 R, 197/98, 335/206 G06c 7/02, HOlh 9/00 235/145 R; 197/98; 335/206, 205, 207, 153, 296

References Cited UNITED STATES PATENTS l/l970 Marchetti 335/207 Primary ExaminerStephen .l. Tomsky Att0rneyEdward L. Bell et a1.

[5 7] ABSTRACT An improved key stem magnet for eliminating magnet migration in a key assembly employing a magnetic actuator. A magnet has a slotted portion extending longitudinally for providing a pair of abutment edges which engage opposing surfaces of a key stem. The abutment edges prevent axial migration of the magnet when mounted in an aperture in the key stem. A pair of parallel, axially extending magnet sidewalls located substantially opposite the slotted portion limit axial rotation of the magnet in the aperture.

10 Claims, 9 Drawing Figures KEYBOA HAVING FROVED MAGNETIC ACTUATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to keyboard devices having one or more key assemblies, each of which is provided with a magnetic actuator element for maintaining the key in a nonactuated position and for actuating an associated switch. Such keyboard devicesare used in a wide variety of applications including, but not limited to, calculators, computers, electronic cash registers, and other devices requiring an interface between an operator and a machine. More specifically, this invention relates to an improved magnetic actuator for such keyboard devices.

2. Description of the Prior Art Keyboard devices are known which employ the principle of magnetic latching and magnetic switch actuation. In a typical keyboard device, such as that disclosed in my copending application Ser. No. 86,678 for Keyboard Having Magnetic Latching and Improved Operator Touch" tiled Nov. 4, 1970, now US. Pat. No. 3,693,123, a plurality of key assemblies are reciprocably received in separate apertures in a mounting plate assembly having an upper mounting plate and a lower base plate. The upper mounting plate is constructed of a material exhibiting low magnetic remanence, e.g., steel, and is provided with an upper cushioning layer and a lower spacing layer, both of resilient material. Each key assembly comprises a key top, a key stem constructed of a nonmagnetic material, a magnet mounted substantially transversely of the key stem below the lower spacing layer in an aperture provided in the key stem, and a return spring positioned between the bottom surface of the key top and the upper surface of the upper mounting plate. the baseplate'is provided with a plurality of apertures, each for reciprocably receiving the lower end of a different key stern, and a plurality of magnetic reed switches, each associated to a different magnet. In an assembled keyboard of the above type, each key assembly is maintained in the nonactuated position by the combined forces provided by the return spring and the magnetic attraction between the magnet and the mounting plate. When a given key assembly is depressed, the magnet carried by the associated key stem is brought into proximity sufficiently close to the associated reed switch to actuate that reed switch. When the actuated key assembly is released, the return spring and the magnetic attraction between the magnet and the mounting plate ensure a return of the key assembly to the nonactuated position.

While the above type of key assembly has been found to function in a satisfactory manner, it has been observed that under certain operating conditions prolonged operation of the individual key assemblies results in migration of the magnets in the stem mounting apertures in a direction transverse to the longitudinal axis of the key stems. In some cases, such migration of individual magnets has been found to result in failure of the associated reed switches to operate properly. In extreme cases, magnets have been observed to completely leave their respective apertures, rendering the associated switches completely inoperative.

SUMMARY OF THE INVENTION The invention disclosed herein comprises an improved key stern magnet for eliminating magnet migration in keyboard assemblies of the type described above. The improved key stem magnet has a slotted portion extending longitudinally thereof which provides a pair of abutment edges which engage opposing surfaces of a key stem when the magnet is mounted in the key stem aperture. The abutment edges prevent axial migration of the magnet in the key stem aperture. A pair of parallel, axially extending magnet sidewalls located substantially opposite the slotted portion are also provided to limit axial rotation of the magnet in the aperture to a range within which the abutment edges exhibit sufficient purchase with the opposing key stem surfaces to prevent axial migration of the magnet.

For a fuller understanding of the nature and advantages of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the keyboard embodying the invention;

FIG. 2 is a sectional view of a single key assembly; FIG. 3 is a front view taken along lines 3-3 of FIG.

FIG. 4 is a top plan view of the improved magnet; FIG. 5 is a rear elevational view of the improved magnet;

FIG. 6 is an end view of the improved magnet;

FIG. 7 is a perspective view of the improved magnet; and

FIGS. 8 and 9 are enlarged partial views showing the magnet in two extreme rotational positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings, FIG. 1 shows a keyboard device generally indicated at 10, which is suitable for use in an electronic calculator and which embodies the invention. As shown in F IG. 1, keyboard 10 has a plurality of numeric keys and function keys 12 grouped in a fashion convenient for the human operator. Each key 12 is mounted on an upper mounting plate 20 for reciprocable motion in a direction substantially normal to the plane of mounting plate 20. Located at the corners of mounting plate 20 are four spacers 211, the lower ends of which each have an internally threaded portion of reduced diameter adapted to be passed through associated openings (not shown) in the corners of a base member 30 for receiving suitable fasteners (not shown).

Mounting plate 20 comprises a three-layered sheet having a plurality of openings therein for receiving a number of key assemblies, described below. As shown most clearly in FIGS. 2 and 3, mounting plate 20 has a central core 23 which may be composed of any material known to those skilled in the art as having low magnetic remanence. Low carbon steel and also soft iron have been found to be highly effective materials from which central core 23 can be constructed.

A cushioning layer 24 of suitable material is adhered to the upper side of central core 23. Cushioning layer 24 may be constructed by any resilient material which provides a cushioned stop for keys 12. Polyurethane foam having vinyl or polyester film on the facing side and adhesive on the underside has been found to be a highly effective material from which cushioning layer 24 may be constructed. Other equally suitable materials will occur to those skilled in the art.

A spacing layer 2% is adhered to the underside of central core 23 by means of a suitable adhesive. Spacing layer 28 provides a maximum desired force for holding a key in the nonactuated rest position and reduces the noise produced by a key when returning to the rest position after release. Spacing layer 28 may be composed of rubber, polyurethane, or the like.

Base member 30 has a number of magnetic reed switches 32, two of which are partially visible in FIG. 1, mounted on the upper surface thereof. It is understood that the number and configuration of reed switches 32 corresponds to the number and arrangement of keys 12 in such a manner that each key 12 has a single reed switch 32 associated thereto.

FIGS. 2 and 3 illustrate a single key assembly 11 which comprises a key top 12 and a key stem 16. Key top 12 has a central opening 13 adapted to receive the upper end of key stem 16. Key top 12 is provided with a conical groove 15 concentric with central opening 13, which is adapted to receive a return spring 22. Key stem 16 has a main body portion 17 and an axially offset lower body portion 1% of reduced diameter. Both key top 12 and key stem 16 may be constructed from any suitable non-magnetic material known to those skilled in the art: ABS (acrylonitrile butadiene styrene) polymer compound has been found to be well suited for molding key tops 12; both Delrin and Celcon acetal compound have been found to be excellent for constructing key stem 16.

As shown in FIG. 2, key assembly 11 is mounted in keyboard for reciprocable movement in a generally vertical direction with main body portion 17 and lower body portion 18 of key stem 16 received by openings in upper mounting plate 20 and base member 30, respectively.

Referring to FIGS. 2-7, a magnet 40 is mounted in a generally circular groove 42 on main body portion 17 of key stem 16 in a direction generally transverse to the longitudinal axis of key stem 16. To facilitate mounting of magnet 40, a slot 44 is formed in main body portion 17 of key stem 16 below circular groove 42 to provide a slightly resilient land 45.

Magnet 40 has a generally cylindrical configuration with a pair of axially extending, opposed land surfaces 50, 60. A pair of substantially parallel wall surfaces 52, 54 join land surface 50 to the cylindrical surface of magnet 40 for a purpose described below. Land surface 60 is provided with a cutaway portion forming a notch having sidewalls 62, 64. The axial distance between sidewalls 62, 64 is slightly larger than the width of key stem 16, shown in phantom in FIGS. 4, 5, to facilitate assembly of the magnet 40 and stem 16. As best shown in FIGS. 8 and 9, land surfaces 52, 54 provide stops for preventing rotation of magnet 40 beyond predetermined maximum angular positions. In FIG. 8, magnet 40 is depicted in a first maximum angular position in which surface 52 engages surface portion 66 of groove 42, thereby preventing further angular rotation in the counter-clockwise direction. In FIG. 9, magnet 40 is depicted in a second maximum angular position in which surface 54 engages surface portion 68 of groove 42, thereby preventing further angular rotation in the clockwise direction. The range of permissible angular rotation employed in the preferred embodiment is chosen to prevent magnet 40 from rotating in either di rection in aperture 42 to a position in which the corners formed by the junction of surfaces 52, 54 with surface 50 engage the lower surface of spacing layer 28 when a key assembly 11 is in the rest position. This prevents highly abrasive contact between these comers and spacing layer 28, thereby promoting long life of the latter element. In other embodiments not employing such a spacing layer 28, the range of maximum permissible angular rotation may be extended, if desired. In such embodiments, this range may be selected to prevent magnet 40 from rotating to a position in which the notch defined by sidewalls 62, 64 lacks sufficient purchase with the opposing sidewalls of stem 16 to prevent axial migration of the magnet 40.

In operation, each key assembly 11 is maintained in the nonactuated or rest position illustrated in FIGS. 2 and 3 primarily by the magnetic force of the attraction between magnet 40 and central core 23, with the assistance of return spring 22. When a key is depressed, the magnetic force of attraction between magnet 40 and central core 23 decreases rapidly with increasing separation between these two elements as key assembly 11 moves in the downward direction, while the restoring force provided by return spring 22 increases as the spring becomes compressed. When the key is released, key assembly 11 is displaced in an upward direction under the influence of return spring 22 and, as the key approaches the rest position, the force of attraction between magnet 40 and central core 23. When key assembly l 1 reaches the rest position illustrated, the magnetic force of attraction attains its maximum value.

With repeated operation, the notch formed by sidewalls 62, 64 of magnet 40 provides abutment edges which prevent axial migration of magnet 40 in groove 42. As noted above, wall surfaces 52, 54 prevent axial rotation of magnet 40 beyond the permissible range so that the abutment edges provide sufficient purchase with the opposing surfaces of key stem 16 to ensure that axial migration of magnet 40 will not take place. This construction offers the further advantage that no cement is required to adhere magnet 40 to key stem 16. Thus, each key assembly 11 can be assembled more quickly and less expensively than other known devices requiring a magnet adhesive.

While the foregoing provides a full disclosure of the preferred embodiment of the invention, it is understood that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is solely defined by the appended claims.

What is claimed is:

1. For use in a magnetic keyboard assembly including a key stem having a magnet mounting aperture, a magnet having a slotted portion extending longitudinally thereof and providing a pair of abutment edges for limiting axial movement of said magnet when mounted in said stem aperture, and means for limiting axial rotation of said magnet within a predetermined range when mounted in said stem aperture.

2. The apparatus of claim 1 wherein said means for limiting axial rotation comprises a longitudinally extending portion of said magnet having a pair of stop surfaces each for engagement with a different portion of the surface of said aperture when said magnet is in a different one of two maximum permissible angular positions.

3. The apparatus of claim 11 wherein said means for limiting axial rotation comprises a pair of raised surfaces of said magnet extending axially thereof, each said surface providing a stop surface for engaging a different portion of the surface of said aperture when said magnet is in a difi'erent one of two maximum permissible angular positions.

The apparatus of claim 3 wherein said pair of raised surfaces is located generally opposite said slotted portion.

5. The apparatus of claim ll wherein said magnet is configured as a cylinder with a pair of longitudinally extending substantially opposed land surfaces, said means for limiting axial rotation comprising a first pair of substantially parallel sidewalls extending from a first one of said land surfaces to the surface of said cylinder, a portion of each said sidewall being engageable with a different portion of the surface of said aperture when said magnet is in a different one of two maximum angular positions, said slotted portion comprising a cutaway portion of the other one of said land surfaces.

6. in a keyboard device comprising a mounting means of magnetic material having low magnetic remanence and having an opening therein; a key assembly including a key stem reciprocably received by said opening and a key top mounted at one end of said stem, said key assembly adapted to be reciprocated between a nonactuated position and an actuated position; said key stem having a middle body portion with an aperture therein; and an elongate magnetic member mounted in said aperture substantially transverse of the body axis of said key stem; the improvement wherein said elongate magnetic member has a longitudinally extending slotted portion providing a pair of abutment edges for engagement with said key stem to limit axial movement of said magnetic member therein, and means for limiting axial rotation of said magnetic member in said aperture within a predetermined range.

7. The apparatus of claim 6 wherein said means for limiting axial rotation comprises a longitudinally extending portion of said magnetic member having a pair of stop surfaces each for engagement with a different portion of the surface area of said aperture when said magnetic member is in a different one of two maximum permissible angular positions.

8. The apparatus of claim 6 wherein said means for limiting axial rotation comprises a pair of raised surfaces of said magnetic member extending axially thereof, each said surface providing a stop surface for engaging a different portion of the surface of said aperture when said magnetic member is in a different one of two maximum permissible angular positions.

9. The apparatus of claim 8 wherein said pair of raised surfaces is located generally opposite said slotted portion.

110. The apparatus of claim 6 wherein said magnetic member is configured as a cylinder with a pair of longitudinally extending substantially opposed land surfaces, said means for limiting axial rotation comprising a first pair of substantially parallel sidewalls extending from a first one of said land surfaces to the surface of said cylinder, a portion of each said sidewall being engageable with a different portion of the surface of said aperture when said magnet is in a different one of two maximum permissible angular positions, said slotted portion comprising a cutaway portion of the other one of said land surfaces. 

1. For use in a magnetic keyboard assembly including a key stem having a magnet mounting aperture, a magnet having a slotted portion extending longitudinally thereof and providing a pair of abutment edges for limiting axial movement of said magnet when mounted in said stem aperture, and means for limiting axial rotation of said magnet within a predetermined range when mounted in said stem aperture.
 2. The apparatus of claim 1 wherein said means for limiting axial rotation comprises a longitudinally extending portion of said magnet having a pair of stop surfaces each for engagement with a different portion of the surface of said aperture when said magnet is in a different one of two maximum permissible angular positions.
 3. The apparatus of claim 1 wherein said means for limiting axial rotation comprises a pair of raised surfaces of said magnet extending axially thereof, each said surface providing a stop surface for engaging a different portion of the surface of said aperture when said magnet is in a different one of two maximum permissible angular positions.
 4. The apparatus of claim 3 wherein said pair of raised surfaces is located generally opposite said slotted portion.
 5. The apparatus of claim 1 wherein said magnet is configured as a cylinder with a pair of longitudinally extending substantially opposed land surfaces, said means for limiting axial rotation comprising a first pair of substantially parallel sidewalls extending from a first one of said land surfaces to the surface of said cylinder, a portion of each said sidewall being engageable with a different portion of the surface of said aperture when said magnet is in a different one of two maximum angular positions, said slotted portion comprising a cutaway portion of the other one of said land surfaces.
 6. In a keyboard device comprising a mounting means of magnetic material having low magnetic remanence and having an opening therein; a key assembly including a key stem reciprocably received by said opening and a key top mounted at one end of said stem, said key assembly adapted to be reciprocated between a nonactuated position and an actuated position; said key stem having a middle body portion with an aperture therein; and an elongate magnetic member mounted in said aperture substantially transversE of the body axis of said key stem; the improvement wherein said elongate magnetic member has a longitudinally extending slotted portion providing a pair of abutment edges for engagement with said key stem to limit axial movement of said magnetic member therein, and means for limiting axial rotation of said magnetic member in said aperture within a predetermined range.
 7. The apparatus of claim 6 wherein said means for limiting axial rotation comprises a longitudinally extending portion of said magnetic member having a pair of stop surfaces each for engagement with a different portion of the surface area of said aperture when said magnetic member is in a different one of two maximum permissible angular positions.
 8. The apparatus of claim 6 wherein said means for limiting axial rotation comprises a pair of raised surfaces of said magnetic member extending axially thereof, each said surface providing a stop surface for engaging a different portion of the surface of said aperture when said magnetic member is in a different one of two maximum permissible angular positions.
 9. The apparatus of claim 8 wherein said pair of raised surfaces is located generally opposite said slotted portion.
 10. The apparatus of claim 6 wherein said magnetic member is configured as a cylinder with a pair of longitudinally extending substantially opposed land surfaces, said means for limiting axial rotation comprising a first pair of substantially parallel sidewalls extending from a first one of said land surfaces to the surface of said cylinder, a portion of each said sidewall being engageable with a different portion of the surface of said aperture when said magnet is in a different one of two maximum permissible angular positions, said slotted portion comprising a cutaway portion of the other one of said land surfaces. 